The invention relates to a method for measuring the thickness of non-circular elongated workpieces to be displaced in the direction of their elongation, said workpieces being in arbitrary and varying angular positions while they are being advanced.
It has become known to set the roll gap in rolling mills for flat products (heavy metal plates, hot metal plates) by means of a closed loop control system. To this end a measuring system is positioned behind the last roll stand, which measuring system continuously measures the thickness and, if desired, the eveness of the rolled product so as to provide an actual value for the control system which then sets the roll gap height and the roll gap geometry by means of respective actuators with a view to dimensional accuracy and flatness of the product.
It is desirable to use closed loop control systems also in mill trains for round products. Sofar this was not possible because measuring systems which are able to measure the true height and width of the rolled rod which may be twisted during advancement are not available.
It has become known to use oscillating or rotating singular axis measuring systems or double axes measuring systems of the adjustable angular position type in wire and rod rolling mills. The rotary measuring system is able to provide for diameter values measured at arbitrarily selected angular positions to be used as actual values. If, however, the true height position and the true width position of the rod differ from the initially defined angular positions due to twist of the product, incorrect measuring values will be obtained. Therefore, such a measuring method cannot be used in a closed loop control system.
Another prior art solution provides a pair of orthogonal measuring systems the angular positions of which may be adjusted simultaneously. Such a measuring system could be used for control if twist of the rolled product would be known and uniform. The prior art measuring system allows to determine the contour of the rolled product within an extremely short time. An operator then would be able to determine the position of the height and width axes of the rolled product by means of a diagram and to set the measuring head in this position. However, this would not allow to recognize whether there has been a change of the filling degree of the roll gap or a twist of the rolled product. If for example the twist angle would change while underfill would remain the same, the measured width would increase provided that the measuring system initially was in its optimal position. An increase of the measured width values, however, would result in an incorrect control of the total system. On the other hand, rotation of the rolled rod from an incorrect to a correct position would result in a measurement erroneously indicating a decrease in width.
A further prior art method uses a single axis measuring system adapted to be positioned under selectable angles, for example along the width of a twisted rod. In case of an increase of the measured values the measuring system performs minor forward and rearward search movements in order to determine whether the increase of the measured values results from a change of the filling degree or from a change of the twist angle. If the latter is true, the measuring system will be positioned under an angle where the diameter of the rod is a minimum. Such a measuring system is also not suited for a control because the measured actual value oscillates at the frequency of the search movement when there is a change of the twist angle.